Condylar hyperactivity, an anatomical variation: a critical integrative review bridging biology, diagnosing, and decision-making in orthognathic surgery.

Unilateral condylar hyperactivity (CH) is a craniofacial condition characterised by excessive growth of one mandibular condylar process that leads to progressive facial asymmetry. Patients commonly require combined orthodontic and surgical interventions to restore function, facial symmetry, and quality of life, posing substantial financial burdens on individuals and healthcare systems. Diagnosis has traditionally relied on clinical and imaging findings, including visible facial asymmetry, enlargement of the mandibular ramus and/or condyle on two-dimensional (2D) and three-dimensional (3D) imaging, and increased metabolic activity on single photon emission computed tomography (SPECT), typically defined as a ≥10% side-to-side difference. Treatment, which depends on the activity level of the condylar tissue and severity of the resulting deformity, can include condylectomy and corrective surgery to correct the mandibular deformity. When CH is not progressing, treatment consists of orthodontic and surgical correction, with condylectomy used selectively. Despite extensive clinical experience, the aetiology of CH remains unclear, limiting the possibility of preventive or orthopaedic treatments. When current knowledge of the clinical features of CH, together with knowledge of temporomandibular joint morphology and metabolism, and cartilage and bone biomechanics, are brought together, there is strong evidence to suggest that CH develops as a result of a mechanical adaptation of the bone and cartilage. This article proposes the reframing of CH as extreme cases of a morphological variation that can lead to functional consequences, depending on severity. This perspective emphasises mechanistic insights that may improve diagnostic precision and guide more effective, biologically-grounded management strategies.